Quirks in characters arent exactly bad, but when they take up a character's entire personality it becomes a problem.
Tharja for instance had her entire character composed of "yandere witch girl", lacking any real development involving a proper backstory or anything outside of that.
Something like Gaius is what works. While he did love candy, there was much more to his character than just that.

Because every unit in Lyn mode other than Sain, Kent, and Florina is effectively useless, both during the mode and in the long.
Also just because a unit is forced doesn't mean it is optimal to train them. Outside of Lyn, Roy is also a very good example of this.

@omegaxis1 Both Falchions were created by Naga by forging two of her fangs into the blades of swords, hence the nickname "Kingsfang". Both blades allow the wielder to fight as if they were a divine dragon themselves, it doesn't give the user Naga's power like the Book of Naga from FE4. The wielder of Falchion can only obtain Naga's power after preforming the Awakening.

Sigurd is ghost Sigurd from the secret event during Gen 2. His lv 40 conversation talks about him wanting to approach Seliph in the way he does in the secret event. Also Deirdre has her memories wiped, meaning she could be from any time outside of chapter 1-3.

Bow Armors from FE4 and 5. I know they aren't playable but seriously, they are armored units locked to bows that don't have pursuit or any skills at all for that matter. You can't get any worse than that.

Same here. Outside of a few people, noone particularly thought she was a good unit. People mostly just joked about how bad she was despite the fact Ewan is way worse. I'm pretty sure I recall people thinking NIno was the best GBA mage or something being a issue though, but never anything with Amelia.

I was not referring to Cav!Kliff, I was referring to the class as a whole. The Cavalier isn't as good as there aren't very many units who can actually function well in the class due to it not receiving growth modifiers, and their no longer as impressive bases. The only units not counting pitch fork reclassing that can function all that well without special treatment to my knowledge are every unit who joins as a member of the Cav line other than Clive, Faye, and Kliff.

This map pretty much requires you to turtle the hell out of it to get through. That's honestly all the advice I can give. Just know that Duma's Gate has to be one of if not the absolute worst designed map in the entire franchise, and it isn't out of place to have trouble with it.

The reason for this is that it would have broken the original book 2 of FE3 even more than it already was, and that game is a mess in terms of balancing if you haven't played it.
Also something I think might be worth noting about FE1 and FE3 was that units had didn't really have to promote at all sometimes. The reason for this is because all stats other than HP capped at 20 and how stat bonuses on promotion worked. The only real benefit of promoting usually was the level reset and mov bonus.
Oh and one more thing. Darros, Roshea, Vyland, Dolph, Macellan, Tomas, Abel, Lena, Maria, and Elice all join promoted unlike in SD. Just sayin.